Witnessing entanglement with trRIXS requires measuring the scattering cross section of a light-driven material, evaluating the transient dynamical structure factors, calculating the QFI, and determining relevant quantum bounds signaling the presence of entanglement for a certain observable (see Fig. REF ). Each step encapsulates a distinct challenge. First, estimating accurate spin fluctuations using trRIXS requires separating the contributions of high-order excitations mediated by the intermediate state of the scattering process. Second, competing time and energy resolution effects imply that the QFI for the instantaneous wavefunctions [1]} cannot be directly extracted by the spectrum at a single time delay and must be deconvolved on the time axis. Third, assessing the entanglement depth requires calculating suitable theoretical bounds for the QFI operator. While the quantum Cramer-Rao bound is well-defined for spin operators in magnetic materials, analytical formulations for general fermionic systems are still lacking [2]}, [3]}.
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